Introduction
Many people may not know that injection molds are actually graded. Different grades of injection molds differ significantly in both quality and mold-making costs.
Clearly defining mold grades can help companies rationally match production needs, control costs, and ensure a balance between product quality and production efficiency. The following is a detailed explanation of the relevant content regarding the classification of injection mold grades.
Currently, the mainstream grading systems in the industry include Chinese national standards/industry grading and the US SPI standard. There are also auxiliary grading methods based on dimensions such as the complexity of mold structure.
China’s mainstream classification
Chinese national standards and industry standards generally adopt a grading method based on expected lifespan and precision , classifying injection molds into four levels. The different levels have clear distinctions in material selection, hardness requirements, and application scenarios.
The first-level mold is a high-precision, long-life mold with an expected life of no less than 1 million cycles. The core precision can reach ±0.005~0.01mm, and the surface needs to achieve a mirror effect with a roughness Ra≤0.02μm.
In terms of material selection, the mold core is usually made of high-quality steel such as H13 and S136. After vacuum heat treatment, the hardness can reach HRC48-52. These molds are mainly used to produce automotive core components, optical lenses, medical precision parts and other products with extremely high requirements for precision and stability.
The secondary mold is a medium-precision, medium-life mold with an expected lifespan of 300,000 to 1,000,000 cycles and an accuracy controlled within ±0.01~0.03mm.
Mold core materials are mostly pre-hardened steels such as 718H and NAK80, which are suitable for mass production of products such as home appliance shells and electronic connectors that require a certain level of precision.
Level 3 molds are classified as ordinary molds, with an expected lifespan of 100,000 to 300,000 cycles, an accuracy of ±0.05mm, and a surface roughness of Ra0.2~0.4μm.
The mold core is made of common steel such as P20 steel and is widely used in the mass production of basic products such as daily necessities and packaging containers that do not have high precision requirements.
Level 4 molds are simple/trial production molds with an expected lifespan of less than 100,000 cycles and lower precision requirements. Their core advantage lies in rapid prototyping.
The mold material is mostly 45 # steel , mainly used for sample verification, small batch trial production and other scenarios, to help companies complete product design verification before formal mass production.
US SPI standard
The American SPI AN-102-78 standard is a widely recognized grading specification in the international mold industry. It is applicable to injection molding machines with clamping force ≤400 tons. It also uses mold life as the core indicator, classifies molds into 5 types, and makes clear provisions for mold base hardness, mold core hardness and precision grade.
The Type 101 mold is a high-precision, long-life mold with an expected life of no less than 1 million cycles. The mold base has a hardness of BHN280 (equivalent to HRC30), and the mold core is made of high-quality steel such as S136 and H13 with a hardness of HRC48-50 and a precision grade of IT5. It is suitable for the production of ultra-large-volume, high-precision products.
The Type 102 mold has an expected lifespan of 500,000 to 1,000,000 cycles. Its hardness indicators are consistent with those of the Type 101 mold, and its precision level is IT6. It is a common choice for mass production scenarios.
The Type 103 mold is a medium-batch production mold with an expected life of 100,000 to 500,000 cycles. The mold base hardness is BHN165 (HRC17), the mold core hardness is HRC30 (HB280), and the precision grade is IT7.
Type 104 molds are suitable for small-batch production, with an expected life of 500 to 100,000 cycles. The mold base and mold core are mostly made of mild steel or aluminum, with a precision grade of IT7-IT8.
The Type 105 mold is a prototype/test mold with an expected lifespan of less than 500 mold cycles. It is made of simple materials such as resin or die casting and is used only for product prototype verification.
In addition to the mainstream classification based on lifespan and precision, the industry also conducts auxiliary classification based on the complexity of the mold structure to further refine the applicable scenarios of the mold.
Among them, the Class A mold has more than 10 complex features, such as multi-slider, hot runner, and three-part parting, and is specially used for the production of ultra-precision products.
Grade B molds contain 2-4 sliders/slanted ejectors and a secondary parting structure, suitable for products with complex structural components for home appliances, etc.
Grade C molds are equipped with 1-2 sliders and a narrow sprue, and can be used for the production of products such as ordinary electronic casings.
Grade D molds are two-plate molds with large sprues and no slider structure. They have the simplest structure and are mainly used for basic products such as daily necessities trays.
Factors for determining mold grading
In the mold grading process, four core factors play a decisive role.
First is lifespan, which directly determines the choice of mold material and heat treatment scheme. It is the primary indicator for grading, and the wear resistance of materials and heat treatment processes corresponding to different lifespan requirements vary significantly.
Secondly, there is the matter of precision. The level of precision affects the dimensional tolerances and surface quality of the product. In particular, precision molds usually require mirror polishing and are equipped with temperature control devices to ensure the stability of precision.
Secondly, there is the material and hardness. The hardness of the mold core and mold base is directly related to the wear resistance and service life of the mold. For example, the hardness of the mold core of the SPI 101 mold must reach HRC48 or above.
Finally, there is the issue of structural complexity. The addition of complex structures such as sliders, angled ejectors, and hot runners increases the grading weight of the mold, and also affects the mold’s manufacturing cost and production cycle.
Final Words
In summary, the grading system for injection molds is relatively complete, with different grading standards each having their own emphasis, but all revolving around actual production needs.
During the selection process, enterprises need to comprehensively consider factors such as product batch size, precision requirements, and material type to accurately match the mold grade in order to maximize production efficiency.
